Ultrasound-triggered hydrogel formation through thiol-norbornene reaction

Ultrasound-initiated thiol-norbornene reaction has been applied to fabricate hydrogels, and the ultrasound conditions in determining the properties of hydrogels have been systematically investigated.

Enzyme-Triggered Hydrogels for Pharmaceutical and Food Applications

Enzyme-mediated polymeric hydrogels are drawing considerable attention in pharmaceutical and food sectors owing to their superior biocompatibility and process controllability under physiological conditions. Enzymes play a significant role in polymeric hydrogel formation through different mechanisms. Oxidases (e.g., horseradish peroxidase and tyrosinase) have demonstrated to drive the crosslinking of gel precursors by oxidizing the phenolic or acrylic moieties to free radicals. Transferases and hydrolases catalyze elongation of biopolymer chains which gradually self-assemble into hydrogels. Still more certain enzymes also participate in hydrogel formation by releasing gelation factors. Enhancement of the desired properties of certain hydrogels through the interior and exterior post-modifications has also been demonstrated by certain enzymes. Hence, in this chapter, the authors explore the different mechanisms of enzyme-mediated hydrogels preparations and its fabrication towards pharmaceutical and food sectors along with the discussion of recent trends and further prospects.

Photo-Polymerization Damage Protection by Hydrogen Sulfide Donors for 3D-Cell Culture Systems Optimization

Photo-polymerized hydrogels are ideally suited for stem-cell based tissue regeneration and three dimensional (3D) bioprinting because they can be highly biocompatible, injectable, easy to use, and their mechanical and physical properties can be controlled. However, photo-polymerization involves the use of potentially toxic photo-initiators, exposure to ultraviolet light radiation, formation of free radicals that trigger the cross-linking reaction, and other events whose effects on cells are not yet fully understood. The purpose of this study was to examine the effects of hydrogen sulfide (H2S) in mitigating cellular toxicity of photo-polymerization caused to resident cells during the process of hydrogel formation. H2S, which is the latest discovered member of the gasotransmitter family of gaseous signalling molecules, has a number of established beneficial properties, including cell protection from oxidative damage both directly (by acting as a scavenger molecule) and indirectly (by inducing the expression of anti-oxidant proteins in the cell). Cells were exposed to slow release H2S treatment using pre-conditioning with glutathione-conjugated-garlic extract in order to mitigate toxicity during the photo-polymerization process of hydrogel formation. The protective effects of the H2S treatment were evaluated in both an enzymatic model and a 3D cell culture system using cell viability as a quantitative indicator. The protective effect of H2S treatment of cells is a promising approach to enhance cell survival in tissue engineering applications requiring photo-polymerized hydrogel scaffolds.

Development of an Amino Sugar-Based Supramolecular Hydrogelator with Reduction Responsiveness

Stimuli-responsive supramolecular hydrogels are a newly emerging class of aqueous soft materials with a wide variety of bioapplications. Here we report a reduction-responsive supramolecular hydrogel constructed from a markedly simple low-molecular-weight hydrogelator, which is developed on the basis of modular molecular design containing a hydrophilic amino sugar and a reduction-responsive nitrophenyl group. The hydrogel formation ability differs significantly between glucosamine- and galactosamine-based self-assembling molecules, which are epimers at the C4 position, and only the glucosamine-based derivative can act as a hydrogelator.